超级铁素体不锈钢组织、性能及其加工行为研究

发布时间：2018-06-20 14:11

本文选题：高铬 + 超级铁素体不锈钢　；参考：《天津大学》2016年博士论文

【摘要】：超级铁素体不锈钢具有优异的耐腐蚀性能,在很多领域可以替代价格昂贵的超级奥氏体不锈钢和镍基合金。但是目前针对超级铁素体不锈钢的理论研究和实际生产经验都很不足,合金元素作用、析出相析出机理尚不明确,低温脆性有待进一步改善。因此,开展超级铁素体不锈钢及其生产、加工的组织、性能方面的研究具有重要的理论意义和工程应用价值。本文系统研究了合金成分、生产工艺、使用技术等对超级铁素体不锈钢组织、性能的影响,重点对不同温度下材料析出行为和材料冲击韧性改善进行了研究。研究发现Cr、Mo元素显著提高材料再结晶温度、耐点蚀和耐硫酸腐蚀性能,Mo元素强烈促进χ相的析出,在Cr、Mo的联合作用下,材料χ相析出温度区间明显扩大,χ相析出方式也由单纯的晶内析出转变为晶界、晶内同时析出。Cr、Mo的合金强化作用非常明显,通过固溶强化和析出强化显著提高材料强度和硬度。Ni元素可以显著提高材料耐硫酸均匀腐蚀性能和材料的冲击韧性。热轧工艺对热轧板和热轧退火板组织性能有显著影响,随着热轧终轧温度的降低,热轧板带状组织内部滑移带增加,形变亚晶内部位错密度升高,热轧板强度、硬度升高。同时热轧终轧温度的降低会使材料再结晶温度降低,再结晶晶粒尺寸减小。热轧后炉冷会促进富Mo的χ相析出,使材料强度、硬度显著升高。材料退火温度显著影响材料再结晶组织和析出相析出温度、尺寸和数量,进而影响退火后性能。随着退火温度的升高,晶粒均匀性越好,晶粒尺寸越大,而表现出的延伸率也逐渐升高,强度、硬度下降,材料冲击韧性也逐渐升高。超级铁素体不锈钢析出相主要包括TiN、NbC、α′相、χ相和σ相。TiN颗粒和NbC颗粒弥散分布在整个材料基体中,在材料生产加工过程中较稳定。α′相典型析出鼻尖温度为475°C;在600°C~1000°C时效过程中,主要析出χ相,χ相为一种亚稳定相,在700°C~950°C之间随着时效时间延长,χ相会逐渐转变为σ相。χ相在晶界和晶内同时析出,而σ相主要在晶界析出,温度升高到1000°C时,主要析出χ相,σ相不析出,且随着时效时间的延长晶界χ相先析出后固溶。激光焊和脉冲TIG焊两种焊接方法得到的焊缝组织均为单相铁素体组织,焊缝都包含中心等轴晶区和边部柱状晶区。脉冲TIG焊缝析出相主要包括Ti和Nb的碳氮化物以及微量的χ相,而激光焊缝析出相主要为TiN。χ相的出现主要是脉冲TIG焊热输入大,焊缝冷却速度慢,高温停留时间更长所致。
[Abstract]:Super Ferritic stainless steel has excellent corrosion resistance and can be used to replace the expensive super austenitic stainless steel and nickel base alloy in many fields. However, the theoretical research and practical production experience of super ferrite stainless steel are very insufficient, the precipitation mechanism of alloy elements and precipitates is not clear, and the low temperature brittleness needs to be further improved. Therefore, the research on super ferrite stainless steel, its production, processing structure and properties has important theoretical significance and engineering application value. In this paper, the effects of alloy composition, production process and application technology on the microstructure and properties of super ferrite stainless steel were studied systematically. The precipitation behavior and impact toughness of super ferrite stainless steel at different temperatures were studied. It has been found that the recrystallization temperature, pitting corrosion resistance and sulphuric acid corrosion resistance of Cr-Mo are significantly increased, and Mo strongly promotes the precipitation of 蠂 phase, and under the combined action of Cr-Mo, The temperature range of 蠂 -phase precipitation is obviously enlarged, and the precipitation mode of 蠂 -phase is changed from pure intragranular precipitation to grain boundary. The alloy strengthening effect is very obvious when the alloy is precipitated at the same time. By means of solution strengthening and precipitation strengthening, the strength and hardness of the material can be improved significantly. The uniform corrosion resistance of the material and the impact toughness of the material can be improved significantly. The hot rolling process has a significant effect on the microstructure and properties of hot rolled and annealed sheet. With the decrease of hot rolling temperature, the slip band inside the strip structure increases, the dislocation density in the deformed sub-crystal increases, the strength and hardness of the hot rolled plate increase. At the same time, the recrystallization temperature and recrystallization grain size decrease with the decrease of rolling temperature. The furnace cooling after hot rolling can promote the 蠂-phase precipitation of Mo-rich materials and increase the strength and hardness of the materials. The annealing temperature has a significant effect on the recrystallization structure and precipitation temperature, size and quantity of precipitates, and then affects the properties after annealing. With the increase of annealing temperature, the better the grain uniformity, the larger the grain size, the higher the elongation, the lower the strength and hardness, and the higher the impact toughness. The precipitated phases of super ferrite stainless steel mainly include TiNn NbC, 伪 'phase, 蠂 phase and 蟽 phase. Tin particles and NbC particles are dispersed in the whole material matrix, which is stable in the process of material production and processing. The typical precipitation temperature of 伪' phase is 475 掳C, and during 600 掳C 1000 掳C aging, 蠂 phase is a kind of metastable phase. With the increase of aging time, 蠂 phase gradually changes into 蟽 phase. 蠂 phase precipitates simultaneously in grain boundary and crystal, and 蟽 phase is mainly precipitated at grain boundary, when temperature rises to 1000 掳C. 蠂 phase is mainly precipitated, 蟽 phase is not precipitated, and with the prolongation of aging time, 蠂 phase precipitates first and then solutes. The weld microstructure obtained by both laser welding and pulsed TIG welding is single-phase ferrite, and the weld contains the central equiaxed region and the edge columnar zone. The precipitated phase of pulsed TIG weld mainly includes Ti and NB carbonitride and trace 蠂 phase, while the phase of laser weld is mainly TiN. 蠂 phase is mainly caused by the large heat input of pulsed TIG welding, the slow cooling rate of weld, and the longer residence time at high temperature.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.71;TG335

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